Used Intel 8th gen based mini PCs seem like a pretty good value. 100-150 bucks for a pc from a somewhat reputable brand (lenovo, dell, hp) with slightly better multi core than N150 and ~6W idle if you manage to get it to stay in C10. Some of them have a low profile pcie slot, like M720q and M920q. Also the CPU is socketed so you could technically upgrade it to e.g. i9-9900K, at least the M920q is known to take one as long as you use a powerful enough PSU. Few of them (at least M920q) also support coreboot due to an Intel Boot Guard vuln which could be fun, I'm planning to look into whether it could be ported to my M720q as well.